> Factor in the various negative externalities of increased commercial and residential rents for others, potential traffic/congestion issues etc., and it seems like Amazon got a sweetheart deal.

I think it's only fair to factor in the various positive externalities. Some of those abatements you mention are for development of the spaces they are occupying, which Amazon has committed to do in the billions. Growth pains almost always exist. In places receiving large amounts of migrants (seriously, Amazon is small number compared to the influx of out-of-state employers moving to other regions) they will experience unquantifiable negatives, but we should not let this detract from the similar unquantifiable positives of economic mobility.